Check on the CaseIH web site. Go to this page then click on "Begin your search for the parts you need right here."http://www.caseih.com/northamerica/PartsService/Pages/search.aspxOn the next screen, type Farmall H and hit "Search". Click on the line "Farmall H Tractor" and do a search for 8518DBX. Is that the part he is looking for? If not, he is probably asking about something else on the same page.

The parts breakdown I found didn't provide a serial number break down. Will include a note to that effect.

Neighbor found the part at a local dealership. Price $50- but the dealer never dismantled the tractor to get the part. Guess dealer figured out he would lose money on the part considering the labor involved.